Method for the recovery of normal paraffins by urea adduction



March 18, 1969 EKCIARLSQN ET AL 3,433,734

METHCD FOR THE RECOVERY OF NORMAL PARAFFINS BY UREA ADDUCTION Sheet Filed June 2, 1967 Fig.2 TWO REACTORS- C075, 00 IVOTOVERLAP 9m H2 he 9H4 Qua Qua n qua Qua 0/1/ ADJACENT c-A TOMS r0724 0F 6 mm o TWO RMCTORS-FfZ-D CUTSOV 04/ 4:42 be (M4 Qua 1m; 5+7 ma 4M9 INVENTORS. EDGAR CARLSOA/ FRANCIS E. WYA/A/E,JR.

March 18, 1969 CARLSON ET AL v 3,433,734

METHOD FOR THE RECOVERY OF NORMAL PARAFFINS BY UREA ADDUCTION Filed June 2, 1967 Sheet mzmroumw ivy/Jaw 1NVENTOR3. MRCWIZSM United States Patent M ABSTRACT OF THE DISCLOSURE A mixture containing normal paraffins together with other materials is subjected to urea adduction in a process which tends to equalize the number of moles of each normal paraffin recovered. The process is performed with a plurality of adductors including an adductor for relatively low molecular weight normal parafiins and an adductor for relatively high molecular weight normal paraffins. The feed stream is subjected to overlapping distillation so that some of the normal paraffin fraction earmarked for the low molecular weight adductor is diverted to the high molecular weight adductor and some of the high molecular weight fraction earmarked for the high molecular Weight adductor is diverted to the low molecular weight adductor. Following adduction, the urea from both adductors is subjected to an eduction step, but the educted normal paraflins are incompletely removed from the urea. The urea from both the low and high molecular weight adductors is intermixed and produces a combined urea stream containing some normal paraflins. The intermixed combined urea stream is then divided and recycled to both the low molecular weight and high molecular weight adductors.

This invention relates to an improved urea adduction process for the separation of normal paraffins from a stream containing them together with other materials Normal paraffins are commonly found in refinery streams. Frequently, normal parafiins comprise only a minor proportion of refinery streams and are usually in admixture in said streams together with a major proportion of other hydrocarbons such as isoparaffins, olefins, naphthenes, and aromatics as well as sulfurand nitrogencontaining materials. When recovered from a refinery stream, these normal paraffins have high utility for a variety of purposes. For example, normal parafiins in the C to C range constitute feedstocks for the production of biodegradable detergents. The method of the present invention can be utilized to separate a wide range of normal paraffins from refinery streams, such as normal paraffins having as low as 6 carbon atoms and as high as 54 carbon atoms, generally, and preferably normal paramns having 9 to 23 carbon atoms. The method of this invention is applicable to the recovery of normal paraflins from refinery streams in which they are present over a wide concentration range, which range can be broadly between about 10 and 50 to 90 percent by weight and preferably between about and percent by weight.

The method of this invention is directed toward the recovery of normal paraflins in a relatively high state of purity from a stream containing them together with other materials. For example, the present method is capable of producing a product normal parafiin stream containing between about 75 and 99 weight percent of normal paraffins, generally, or preferably between about 94 and 99 or close to 100 weight percent of normal paraflins. In order to achieve this state of purity, it is a feature of the 3,433,734 Patented Mar. 18, 1969 present method that the quantity of urea charged to the adductor reactor is insuflicient to recover all the normal paraffins present in the charge stream. The presence of a large excess of non-adducted normal'paraflins in the system is thereby assured and this condition minimizes the adduction of molecules other than normal paraffins which would be adducted to a significant degree if there were a dearth of normal paraflins. Molecules which are less preferentially adductable than normal paraffins and which tend to be adducted only if there is a scarcity of normal parafiins include long chain molecules wherein the major portion of the molecule is normal parafiinic but some portion of the molecule has a functional group or unsaturation.

Although the present method does not contemplate adducting all the normal parafiins present in a stream, it is a feature of the invention that substantially all or at least a very high proportion of the urea which is employed participates in adduct formation. The reason that at least a very high proportion of the urea introduced should become involved in adduct formation is that urea and urea adduct impart a high viscosity to fluid streams handled in the process and the viscosity of said streams increases with the quantity of urea and urea adduct present. Therefore, presence of urea which is not utilized in adduct formation imparts an unnecessarily high viscosity to fluid streams in the system without a correspondingly high recovery of normal paraffins. Since a significant portion of the energy consumption of the process is expended in the pumping, agitating, deliquoring, and other handling of urea, adduct and urea-containing slurries, if the process is to have a high ratio of normal parafiin recovery to energy expenditure it is important to avoid circulation in the system of urea which does not contribute to recovery of normal parafiin.

As the adduction temperature decreases, the percentage of urea which forms a complex in the presence of the excess of normal paraffins present tends to increase until nearly complete adduction of urea is approached. However, it is undesirable to employ too low a temperature for adduction because at lower temperatures the tendency for molecules other than normal parafiins to adduct increases. Therefore, the adduction temperature is established by balancing the greatest possible adduction of urea against the highest possible normal paraffin purity in the product and can range from about 0 to 150 F.

As indicated, it is a feature of the present process that a much higher proportion of the urea than the normal paraffins introduced to the process participates in the adduction reaction. Between about and close to 100 weight percent of the urea introduced is utilized in adduct formation and preferably between about and 99 weight percent of the urea added is so utilized.

The urea forms adducts with the normal paraffins by developing a clathrate or lattice-like structure around the various normal parafiin molecules present in the system. The stability of the urea complexes formed varies directly with normal paraffin chain length and inversely with the vapor pressure of the included compound. Therefore, when the adduction reaction occurs in the presence of an excess of a mixture of normal parafiins having a variety of chain lengths and each in equal molal quantity, the highest molecular weight normal parafiin in the system will account for the greatest number of moles adducted, the next highest molecular weight normal paraffin will account for the next greatest number of moles adducted, and the lowest molecular weight normal parafiin will tend to account for the smallest number of moles tadducted. FIGURE 1 is a schema-tic diagram showing the molecular weight distribution of normal paraffins recovered in a single reactor wherein the quantity of urea is insufiicient to adduct all the normal parafiins present, assuming that the charge stream comprises C to C normal paraflins, each in equal quantity by weight.

As indicated in FIGURE 1, when an adduction reactor contains a mixture of normal paraffins in the presence of insufficient urea to accomplish adduction of all the normal parafiins present, the number of moles of each normal parafiin adducted and separated from the mixture tends to decrease at lower molecular weights. FIGURE 1 shows that this phenomenon tends to produce a great disuniformity in the number of moles of the various normal parafiins recovered since the molar recovery of each relatively high molecular weight normal parafiin is considerably greater than the molar recovery of each relatively low molecular weight normal paraffin.

In accordance with the present invention, a plurality of normal parafiins of selected carbon number in a charge stream is recovered in a more nearly balanced or equalized molar distribution in the product by utilizing a plurality of adduction reactors. The charge stream containing the normal parafiins to be recovered is cut into a plurality of fractions and each fraction is charged to a separate adduction reactor. The molar recovery of one or more selected relatively low molecular weight normal paratfins can be enhanced by this method to be comparable to the molar recovery of the highest molecular weight normal paraffins charged to the system. For example, when treating a charge stream containing C to C normal parafiins, if it is desired to enhance the number of moles of C recovered the charge is divided into two fractions, a relatively low molecular weight fraction comprising C to C hydrocarbons and a relatively high molecular weight fraction comprising C to C normal hydrocarbons. The lower molecular weight fraction is charged to a first adductor reactor operated at a relatively low temperature and the higher molecular weight fraction is charged to a second adductor reactor operated at a higher temperature. Since the C normal hydrocarbon is the highest molecular weight normal hydrocarbon in the low molecular weight reactor, it will be the normal parafiin which is adducted to the greatest extent in the low molecular weight reactor. Similiarly, since the C is the normal parafiin having the highest molecular weight in the high molecular weight reactor, it will be the normal paraflin which is adducted to the greatest extent in the high molecular weight reactor. FIGURE 2 schematically illustrates the number of moles of each normal paraffin recovered in the two reactor system, curve A representing the low molecular weight reactor and curve B representing the high molecular weight reactor.

Comparing FIGURES 1 and 2, it is seen that in the single adductor reactor system represented by FIGURE 1 the moles of C normal parafiin recovered is only about half of the number of moles of C normal parafiin recovered whereas in the dual adductor reactor system represented by FIGURE 2 the moles of C normal paraffin is not merely equal to but is shown to be greater than the moles of C normal paraffin recovered, even though the charge to the single reactor system of FIGURE 1 and the charge to the double reactor system of FIGURE 2 is the same and contains each molecular weight normal hydrocarbon indicated in substantially equal weight proportion. Following is the reason that in a dual reactor system the moles of (3 recovered is actually greater than the moles of C recovered. Each mole of a relatively high molecular weight normal parafiin requires a greater number of moles of urea to form a complex than is required by a normal paraflin of lower molecular weight. For example, normal C H combines with 21 moles of urea, normal C H with 12 moles, normal C H with 8.3 moles, and normal C H with 6 moles. Therefore, in the dual reactor system of FIGURE 2, if substantially equal quantities of urea are supplied to each reactor, said quantity of urea being considerably less than the quantity required to form a complex with all the normal parafiins present in each reactor, and substantially all the urea charged is consumed in adduct formation, then the number of moles of normal parafiins adducted in the low molecular weight reactor will be greater than the number of moles of normal parafiins adducted in the high molecular weight reactor, A comparison of curves A and B in FIGURE 2 therefore indicates that more moles of O to C normal parafiins are recovered as compared to the moles of C to C recovered.

When utilizing a plurality of reactors, it is highly disadvantageous to attempt to overcome the unbalance in the number of moles recovered in each reactor by excessive adjustment of the ratio of urea to normal paraflin charged to the various adductor reactors in the system. The molar ratio of urea to normal parafiin charged to each adductor reactor should be established only by the single criterion that in any adduction system there is a particular ratio of urea charge to normal paraflin charge at which there is an optimum number of moles of normal parafiin adducted per mole of urea charged. As explained earlier, it is important to obtain the maximum recovery of normal paraffin per mole of urea charged because the viscosity of ureacontaining slurries is high and tends to increase with ure concentration, requiring high energy expenditure in pumping. For example, consider that about 2.0 pounds of urea per pound of normal parafiin is charged to each of the two reactors represented by FIGURE 2, and at this ratio there is an optimum recovery of normal paraffin in each reactor for each mole of urea charged. Now, if a reduced quantity of urea were added to the low molecular weight reactor and an equal increase in urea is added to the high molecular weight reactor the imbalance in the number of moles of normal parafiin adducted in the two reactors might be corrected but if the urea adjustment required is excessive the imbalance correction is achieved at the price of incurring less than optimum recovery of normal parafiin per mole of urea in each reactor. If optimum normal parafiin recovery is achieved in each reactor at a ratio of 2.0 pounds of urea charge per pound of normal paraffin charge, at a lower ratio of, say 1.9, more pounds of urea will be required to recover a mole of normal parafiin in each reactor, thereby increasing the process energy consumption per mole of normal parafiin recovered. If a higher ratio of, say 2.1 or more is used, the reactor having the higher urea concentration will tend to become excessively viscous, perhaps necessitating special equipment to agitate, pump or separate solids from the slurry, or equip ment may become entirely inoperable.

In accordance with this invention most or all of the imbalance in the total number of moles of normal parafiin adducted in the various reactors of a multireactor system is corrected without resorting to disruption of the optimum ratio of urea to normal paraffin in each reactor. According to the method of this invention the imbalance is corrected by means of two separate process steps both of which tend to correct the imbalance and which function interdependently to this end, although each step can be independently employed in the absence of the other to correct the imbalance.

The first of the two cooperative process steps is the charging of feed stream fractions to each adjacent pair of adduction reactors operated in parallel in which the normal paraffin components overlap each other to an extent necessary to completely or partially correct the imbalance in production of selected normal paraffins. For example, of the normal paraffin fraction earmarked for the low molecular weight reactor, between about 5 and 25 weight percent, generally, or between about 10 and 20 weight percent, preferably, is charged to the high molecular weight reactor. Similarly, of the normal parafi'in fraction earmarked for the high molecular weight reactor, between about 5 and 25 weight percent, generally or between about 10 and 20 weight percent, preferably, is charged to the low molecular weight reactor. In a two reactor system to which a refinery stream is charged containing substantially equal amounts of C to C normal paraffins wherein it is desired to tend to equalize the production of C normal paraflin and C normal parafiin, the charge stream would ordinarily be fractionated by distillation into two approximately equal fractions, the first fraction containing C, to C normal paramns and charged to the low molecular weight reactor, and the second fraction containing C to C normal paraflins and charged to the high molecular weight reactor. In a system such as this, the product recovery corresponds to curves A and B of FIG URE 2. Curve A represents the product recovery from the low molecular Weight reactor and curve B represents the product recovery from the high molecular weight reactor. However, a comparison of curves A and B shows that generally more moles of C to C normal parafiins are recovered than moles of C to C normal paratfins, and specifically shows that more moles of C normal paraflins are recovered than C normal paraflins.

In accordance with the overlapping distillation step of this invention, C to C normal parafiin is still charged to the low molecular weight reactor and C to C normal paraffin is still charged to the high molecular weight reactor. However, the feed stock distillation is performed so that a portion of the lower molecular Weight normal parafiins of the C to C cut is charged to the high molecular weight reactor. For example, a portion of the C and C normal parafiins which would have been destined for the low molecular weight reactor is included with the C to C charge to the high molecular weight reactor. If it were desired, some C normal parafiin could also be charged to the high molecular weight reactor. Since it represents the highest molecular weight material charged to the C to C reactor, the overlapping C to C normal paraffin portion would have adducted to a very high degree in the low molecular weight reactor. But, since it represents the lowest molecular weight material charged to the C to C reactor, the same C to C normal parafiin portion will be adducted to a much lower degree in the high molecular weight reactor. As a result, a reduced amount of C to C normal paraffin will be adducted in the over-all system. Similarly, the overlapping distillation can be performed so that some of the lowest molecular weight material ordinarily charged to the highest molecular weight reactor is diverted to the lower molecular weight reactor. While this material would have been the least selectively adducted in the high molecular weight reactor it becomes the most selectively adducted material in the low molecular weight reactor. Therefore, if a portion of the C material is diverted from the high molecular weight reactor to the low molecular weight reactor, the greater tendency for adduction thereof in the low molecular weight reactor will result in an increased amount of C adducted in the over-all system.

FIGURE 3 represents an adduction process similar to that illustrated in FIGURE 2 except for an overlapping distillation in preparing the feeds for each reactor. In the process of FIGURE 2, C to C material was charged to the lower molecular weight reactor and C to C material was charged to the high molecular weight reactor with no substantial overlapping of said feed stocks. The process of FIGURE 3 is the same as that of FIGURE 2 except that some of the C destined for the lower molecular weight reactor is diverted to the high molecular weight reactor while some of the C material destined for the high molecular weight reactor is diverted to the low molecular weight reactor. The number of overlapping moles of C and C normal parafiins is suflicient to overcome at least some of the imbalance in the normal parafiin production in the system.

In FIGURE 3, the material adducted in the low molecular weight reactor is indicated by the solid line C while the material adducted in the high molecular weight reactor is indicated by the solid line D. The total C and C material adducted in both reactors is indicated by the dashed lines. FIGURE 2 shows that a great deal more C material than C material is adducted in the absence of the overlapping distillation step of this invention. In sharp contrast, the dashed lines of FIGURE 3 show that about the same quantity of C and C material is adducted when the overlapping distillation step of this invention is utilized in preparing the feed streams to each reactor. A comparison of FIGURES 2 and 3 clearly shows the great advantage of the overlapping distillation step of this invention.

In the second feature of the multiadductor reactor system of this invention the normal paraffin-urea adduct from all the reactors is charged to a common eductor chamber. The normal parafiins are educted from the urea in said chamber by the application of heat, eduction temperatures being higher than adduction temperatures, and the normal parafiins are then separated from the urea by a suitable means such as filtration or centrifuging. However, a significant quantity of educted normal paraflin remains entrained in the educted urea following the filtration or centrifuging operation and is commonly removed therefrom by washing with a suitable solvent for the educted paraflins. The composition of the normal parafl'lns entrained in the urea corresponds to the composition of th normal paraflin product. Since there is substantially percent urea recycle in the process, in the second feature of this invention the entrained normal paraffins are either not washed from the educted urea or are washed only to a limited extent so that suflicient normal paraifins remain entrained therein to overcome upon recycle a substantial amount of the imbalance in normal paraffin production. In this manner, entrained C to C normal paraflins are recycled to both the high molecular weight reactor and the low molecular weight reactor together with urea. The entrained normal paraifins which are recycled with the urea constitute between about 1 and 50 percent by weight, generally, and between about 1 and 10 percent by weight, preferably, of the total normal paraflins adducted in both reactors. Recycle to the low molecular weight reactor will advantageously further correct the imbalance in normal paraflin production between the two reactors because the recycled C to C normal paraflins will adduct therein to the greatest extent while the C to C normal parafiins will adduct therein to a more limited extent. Similarly, recycle of C to C material to the high molecular weight reactor results primarily in readduction of C to C material with very little readduction of C to C material. The recycle operation therefore tends to increase production of C to C material at the expense of C to C material. As shown in FIGURE 2, an increase in production of C to C material at the expense of C to (1 material will tend to improve the imbalance between these two fractions in the process.

As indicated earlier, the overlapping feed distillation feature of this invention and the recycle feature of this invention can each be advantageously utilized in the absence of the other. However, when both are utilized in the same process they exert cooperative effects in tending to correct the imbalance in parafiin production in a multiadductor system. Comparing FIGURE 3 with FIGURE 2, it is seen that the overlapping distillation step tends to equalize relative production of those parafiins whose proportion in the product is most disparate, without substantially eifecting relative production of the other paraflins. The recycle feature of this invention on the other hand effects relative production of the total products from each adductor. As shown in FIGURE 2, the production of material from the high molecular weight adductor is lower overall than the production of material from the low molecular weight adductor. As explained above, the recycle feature tends to increase the entire range of material initially produced in the high molecular weight adductor relative to the entire range of material initially produced in the low molecular weight adductor. Therefore there is a clear cooperative effect in regard to product distribution between the two features of this invention.

This invention is illustrated in more detail in the specific process illustrated in regard to the flow diagram of FIGURE 4. Referring to FIGURE 4, a refinery stream which contains C to C normal paraflins, together with a major proportion of other hydrocarbons, is charged to distillation column 10 through line 12. A stream which can broadly contain between about 10 and 90 weight percent but which specifically contains between about and 45 weight percent of normal paraffirts in the C to C range plus some C and C normal parafiins is removed from the fractionator and charged to low molecular weight adduct reactor 18 through line 20. Another stream which can broadly contain between about 10 and 90 weight percent but which specifically contains between about 15 and 45 weight percent of C to C plus some C and C normal paraflins is charged to high molecular weight reactor 22 through line 24. Any suitable activator such as any alcohol in the series from methanol to octanol, or another activator such as methylene chloride or acetonitrile is added to adduct reactors 18 and 22 through lines 26 and 28, respectively. There is generally 3 to weight percent alcohol activator added based on the urea present, and preferably 5 to 6 weight percent. If there is no water in the feed, between about 0.001 to 5.0 and preferably about 0.003 weight percent of water based on the urea should be added.

Low molecular weight adduct reactor 18 is operated at specifically between about 125 and 140 F. Recycled urea is charged to each reactor through line 30. Reactor feeds containing a relatively high concentration of normal parafiins must contain a diluent to obtain operable urea concentrations. Suitable diluents include recycle filtrate obtained from the centrifuge filtrate or recycle raffinate obtained from the rafifinate fractionation, both of which are discussed below. A suitable diluent for the feed to high molecular weight adduct reactor 22 is the filtrate from adduct centrifuge 36 which is recycled through line 37. Suitable diluents for the feed to low molecular weight adduct reactor 18 are the filtrate from adduct centrifuge 32 which is recycled through line 33 or the relatively high molecular weight fraction from raffinate farctionator 52 which is recycled through line 53-. Each of these recycle streams will tend to increase the concentration of the low molecular weight material in each adductor and thereby tend to increase the amount of low molecular weight material which is adducted therein.

The slurry from reactor 18 is charged to centrifuge 32 through line 34 and the slurry from reactor 22 is charged to centrifuge 36 through line 38. The slurry charge to each centrifuge contains about 10 to 40 weight percent, generally, and specifically about 25 to weight percent of urea. The centrifuges separate the urea adduct from nonadducted feed hydrocanbons, or raffinate. After raffinate removal, wash liquid is charged to the centrifuges from line 58 to remove remaining raffinate from the cake. Urea adduct cake is removed from centrifuge 32 through line and from centrifuge 36 through line 42. Rafiinate, or nonadducted feed hydrocarbons, together with part or all of the wash liquid is referred to as filtrate and is removed from the centrifuges through lines 44 and 46. Lines 44 and 46 join to form header 48 'which contains rafiinate, adduct wash, activator, urea adduct and urea. The filtrate is water washed in chamber 50 to decompose traces of urea adduct, recover the activator and remove traces of urea and is then sent to raffinate fractionator 52 through line 54 where raffinate is removed from the process through line 56 and wash liquid is removed through line 58 for return to centrifuges 32 and 36. Wash liquid may be recycled at the centrifuges through lines 60 and 62. The wash liquid is a hydrocarbon or other liquid which is essentially nonadductable with urea and separable from the filtrate having a boiling range lower or higher, but preferably lower, than that of the normal parafiin product. Typical wash liquids are in the boiling range of toluene. Either relatively pure toluene, cycloparaffins or paratfins can be used or mixtures of these hydrocarbons in the correct boiling range.

Adduct cake from centrifuges 3-2 and 36 and lines 40 and 42 is fed to common header 64 whence it flows into educt reactor 66. The adduct cake contains urea-normal paraffin adduct together with activator and nonnormal hydrocarbon impurities from the feed. The adduct cake is slurried in educt filtrate charged through line 68 and educt wash hydrocarbons charged through line 70 to maintain the urea concentration in the range of 10 to 40 weight percent, generally, and preferably 25 to 35 weight percent. In educt reactor 66 the slurry is subjected to a temperature of to 225 F., generally, and preferably to F. and most of the eduction or release of the normal paraffin from the adduct occurs there.

The educt slurry is then charged through line 72 to centrifuge 74 wherein educted urea crystals are separated from the normal paralfins. The educt slurry charged to centrifuge 74 contains urea, normal parafiins, activator, nonnormal hydrocarbons and recycle wash liquid. The temperature in the centrifuge is regulated to prevent cooling and consequent readduction of normal parafiins and urea. The educt slurry wash to normal paraffin ratio is regulated between 0.521 and 10: 1, generally, and preferably 1:1 and 4:1 by regulating recycle Wash stream 76 and educt wash stream 70. Wash liquid is charged directly to educt centrifgue 74 through line 78 to wash entrained educted normal parafiins from the urea crystals in the centrifuge. The washed urea crystals, or educt cake containing some wash liquid and activator is recycled to the adductor reactors through line 30. -If the urea crystals are incompletely washed, or if no wash liquid is charged through line 78, the recycled educt cake will carry back to the adductor reactors a stream of entrained educted normal paraffins whose normal parafiin components are in the same proportion as in the normal paraffin product of the process.

Educt centrifuge filtrate not used for reslurrying the adduct cake contains the desired normal parafiins. This filtrate containing normal parafiins, activator, urea traces, wash liquid, and nonnormal hydrocarbons is discharged through line 80 to activator recovery chamber 82 where it is water washed to recover activator and urea traces. The filtrate is then changed to 'wash recovery fractionator 84 through line 86. Wash liquid is recovered overhead through line 70. The normal paraffin product stream is removed from the process through line 88 and can comprise 90 to 99 percent by weight of normal parafiins.

Various changes and modifications can be made Without departing from the spirit of this invention or the scope thereof as deflned in the following claims.

We claim:

1. A process comprising fractionating a feed stream comprising normal parafiins together with other materials into at least one fraction containing relatively low molecular weight normal paraflin and at least one fraction containing relatively high molecular weight normal paraffin, said high molecular weight fraction containing an overlapping portion of said low molecular weight normal paraffin, said low molecular weight fraction containing an overlapping portion of said high molecular weight normal parafiin, charging said low molecular weight fraction together with urea to a first normal paraffin-urea adductor reactor, charging said high molecular weight fraction together with urea to a second normal paraffin-urea adductor reactor, the quantity of urea charged to each of said adductor reactors being insufficient to adduct all of the normal parafiins charged thereto, discharging normal paraffin-urea adduct from each of said adductor reactors, and educting both said low molecular weight and said high molecular weight normal paraffin from its urea adduct.

2. The process of claim 1 wherein between about 5 and 25 weight percent of the normal paraffin in said low molecular weight fraction overlaps said high molecular weight fraction and wherein between about 5 and 25 weight percent of the normal paraffin in said high molecular weight fraction overlaps said low molecular weight fraction.

3. The process of claim 1 wherein between about and Wight percent of the normal paraffin in said low molecular weight fraction overlaps said high molecular weight fraction and wherein between about 10 and 20 weight percent of the normal paraffin in said high molecular weight fraction overlaps said low molecular weight fraction.

4. The process of claim 1 wherein the ratio of urea to normal paraffin charged to each of said adductor reactors is adapted to adduct substantially an optimum number of moles of normal paraffin per mole of urea.

5. The process of claim 1 including the step of washing a mixture of the educted urea derived from said first and said second adduction reactors to remove entrained normal paraffin therefrom, and recycling washed urea to said first and said second adduction reactors.

6. The process of claim 1 wherein said feed stream comprises between about 10 and 90 weight percent of normal paraffin.

7. The process of claim 1 wherein said feed stream comprises between about 15 and 45 weight percent of normalparaflin.

8. The process of claim 1 wherein said feed stream comprises between about .15 and 45 weight percent of normal paraffin in the C to C range.

9. The process of claim 1 wherein between about 75 and 100 weight percent of the urea charged to each reactor is adducted.

10. A process comprising fractionating a feed stream comprising normal paraflins together with other hydrocarbons into at least one fraction containing relatively low molecular weight normal paraffin and at least one fraction containing relatively high molecular weight normal paraffin with said high molecular weight fraction con taining an overlapping portion of said low molecular weight normal paraffin and said low molecular weight fraction containing an overlapping portion of said high molecular weight fraction, charging said low molecular weight fraction together with urea to a first normal paraffin-urea adductor reactor, charging said high molecular weight fraction together with urea to a second nor-mal paraffin-urea adductor reactor, the quantity of urea charged to each of said adductor reactors being insufficient to adduct all of the normal paraffin charged thereto, discharging normal paraffin-urea adduct from each of said adductor reactors and educting both said low molecular weight and said high molecular weight normal paraffin from the urea adduct containing it, partially separating educted normal panaffin from educted urea permitting a portion of the educted normal paraffin to remain entrained in said urea, and recycling a mixture of urea together with entrained normal parafiin derived from both said first and said second adductor reactors back to said first and said second adductor reactors.

11. The process of claim 10 wherein between about 5 and weight percent of the normal paraffin in said low molecular weight fraction overlaps said high molecular weight fraction and wherein between about 5 to 25 weight percent of the normal paraffin in said high molecular weight fraction overlaps said low molecular weight fraction.

12. The process of claim 10 wherein between about 10 and 20 weight percent of the normal paraffin in said low molecular weight fraction overlaps said high molecular weight fraction and wherein between about 10 and 20 weight percent of the normal paraffin in said high molecular weight fraction overlaps said low molecular weight fraction.

13. The process of claim 10 wherein the separation of educted normal paraffin from educted urea includes the step of washing a portion of the educted normal par-afiin I from the educted urea.

14. The process of claim 10 wherein the ratio of urea to normal paraffin charged to each adductor is adapted to adduct substantially an optimum number of moles of normal paraffin per mole of urea.

15. The process of claim 10 wherein said feed stream comprises between about 10 and weight percent of normal paraffin.

16. The process of claim 10 wherein said feed stream comprises between about 15 and 45 weight percent of normal paraffin.

17. The process of claim 10 wherein said feed stream comprises between about 15 and 45 weight percent of normal paraffin in the C to C range.

18. The process of claim 10 wherein between about 75 and weight percent of the urea charged to each reactor is adducted.

19. A process for recovering normal paraflins from a feed stream by urea adduction comprising fractionating said feed stream comprising between about 15 and 45 weight percent of normal paraflins together with other hydrocarbons into at least one fraction containing relatively low molecular weight normal paraflins and at least one fraction containing relatively high molecular weight normal paraflins with said high molecular weight fraction containing an overlapping portion of said low molecular weight normal paraflins comprising between about \10 and 20 weight percent of the normal paraffin of said low molecular weight fraction, said low molecular weight fraction containing an overlapping portion of said high molecular weight normal paraflins comprising between about 10 and 20 weight percent of the normal paraffin of said high molecular weight fraction, charging said low molecular weight fraction together with recycled urea to a first normal paraffin-urea adductor reactor, charging said high molecular weight fraction together with recycled urea to a second normal paraffin-urea adductor reactor, the quantity of urea charged to each of said adductor reactors being insufficient to adduct all of the normal paraffin charged thereto, the ratio of urea to normal paraffin in each reactor being adapted to adduct substantially an optimum number of moles of normal paraffin per mole of urea, discharging normal paraffin-urea adduct from each of said adductor reactors and educting both said low molecular weight and said high molecular weight normal paraflins from the urea adducts containing them, partially separating educted normal paraflins from educted urea but permitting a portion of the educted normal paraflins to remain entrained in said urea, and recycling a mixture of urea together with entrained normal paraflins derived from both said first and second adductor reactors back to said first and said second adductor reactors.

References Cited UNITED STATES PATENTS 2,913,390 11/1959 Brunstrum 208-25 3,328,313 6/1967 DelloW 208308 HERBERT LEVINE, Primary Examiner.

U.S. Cl. X.R. 20825 

